Baby Chicens dying

This is my first time trying to raise baby chickens, but we have done really good up until this week. The chicks turned 8 weeks old and now we are loosing a chicken a day. It started with our two little Bantums (hubby thought that maybe our rooster had attacked because they were so small) then yesterday we lost a Rock?? and today I watched as another died. The one this morning sat down and stated rocking back and forth then just fell over dead.

I am so confused as to what is going on. I was hoping that perhaps someone on here would have some advise. I have read through about the feeding and housing and we are doing all of that correctly, and like I said it just started this week.

Let's think like a diagnostitician. What has changed in the last week for them. Weather? Food? Are they free ranging or in a run, or both? Did anyone spray for weeds at your house or your neighbors where they might have eaten? Check their food, is there any evidence of mold or possible other bacteria. Check each one thoroughly and look for any signs of illness, mites, fleas, etc. Are any of them still acting strange, lethargic, etc.

I don't know what could be wrong but if we get all the possible info we might be able to find some answers together.

I don't know what kind of property or neighbors you have, but could it be that they are eating buggies contaminated with pesticides? We don't use poison for mice because then the hawks and cats could get sick. What kind of plants do they have access to? Some plants are toxic for chickens. Are your chickens confined a lot and how is the ventilation? Do you have any pictures of their environment we can look over to get a better idea of what the issue might be?

They were inside until Friday of last week. Then hubby moved them to an outside run for the day and I brought them back into there "box" for the evening until Tuesday. We lost 2 hens on Sunday, 1 in the morning and 1 in the evening. On Tuesday night we put the "box" into the run and the next afternoon the 2nd Bantum died. Last night, I decided to make a make shift coop on our back porch. completely enclosed with poultry netting and we kept the Rooster separate from them all night. Hubby said that he was in "time out". We put the rooster in the make shift coop on the porch this morning and within 30 mins the other Hen was off her feet and rocking back and forth, then 10 mins later she fell over.

The outside run is open floor so that they can scratch, and I wonder if maybe they had gotten a bug or two that was poisoned. Because they were doing great and looked very healthy up until they died.

We started out with 3 Rhode Island Reds (1 being a Rooster), 2 Bantums, 4 Bared Rock, and a couple others that I don't know what they were. Both Bantums and 2 Barred Rocks have died.